Effects of the number and position of functional leaves on yield traits of rice under different nitrogen levels

Objectives The functional leaves play key roles for the nutrient translocation from vegetative organs to spikes of rice. The paper studied the effects of different number and positions of functional leaves on the panicle characteristics under different nitrogen levels, so as to provide more scientific and reasonable guidance for the actual production of rice.

Methods Taking early-maturing late japonicas ‘Zhendao 11’ as material, a field experiment was conducted in Jiangsu Province. Five nitrogen levels (N 0, 90, 180, 270, 360 kg/hm²) were set up as the main treatments of N0, N90, N180, N270 and N360, and high and low transplanting densities of 32.5 × 10⁴ and 25.5 × 10⁴ hill/hm² as the secondary treatments (HD and LD). At heading stage of rice, panicles with the same size were selected and labeled in each plot. From the panicle downward, the leaves were pruned respectively as: the last 1st (−T), the last 2nd (−T2), the last 3rd (−T3), the last 1st+2nd (−T1+2), the last 1st+3rd (−T1+3), the last 2nd+3rd (−T2+3), the last three (−T1+2+3), and non-pruned (−T0, control), totally 8 pruning treatments. At maturity stage, representative plants were selected to measure the yield components. The seed setting percentage and the superior 1000-grains-weight and the inferior 1000-grains-weight were recorded in each panicles under each pruning treatments.

Results Compared with N0, N application significantly increased the pantcle length and the number of per panicle, but not in panicle length, panicle branch number and weight per panicle among different nitrogen levels (N0, 90, 180, 270, 360 kg/hm²). Under N90, N180 and N270, with the increasing of the stalk position from the top to the base of panicle, the number of grains per branch increased first and then decreased. The results of leaf pruning under the two cultivation densities were similar, indicating the stability of the effect of N level on panicle traits. There was no significant effect on the weight of single spike when the last 1st, 2nd and 3rd leaves was pruned alone, while that was decreased by 5.5%−10.3% with any 2 or 3 leaves pruned together, and when the three leaves were all pruned, that was decreased by 24.6%. Under the same pruning treatment, the decline ratio of weight per panicle increased with the increase of nitrogen level. The analysis of the generalized linear model showed that under different leaf position pruning, the model performance to explain the falling ratio of weight per panicle is: seed setting percentage (SP) > SP, 1000-grain weight of superior spikelets (S) and 1000-grain weight of inferior spikelets (I), in which SP, S, I composite model > I, S composite model.

Conclusions The nitrogen level affects the spike length, number of branches per panicle, number of grains per branch, seed setting percentage and 1000-grain weight, and then the weight of per panicle. Fewer functional leaves after anthesis leads to lower panicle weight, and the lower the higher the nitrogen level. When the number of functional leaves is constant, leaf position does not affect the single spike weight. The position of functional leaves after anthesis affect the single panicle weight of rice by influencing SP, SP and S, SP and I, I and S in turn.